<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Math Operations</title>
    <script type="text/javascript" src="./Demo01.js"></script>
</head>  
<body>
    <form action="" name="myform" id="myform">
        <input type="text" name="num1" id="num1" placeholder="输入第一个数">
        <input type="text" name="num2" id="num2" placeholder="输入第二个数">
        <select id="operationSelect">
            <option value="add">加</option>
            <option value="subtract">减</option>
            <option value="multiply">乘</option>
            <option value="divide">除</option>
        </select>
        <input type="button" value="计算" onclick="calculate()">
        <input type="text" name="result" id="result" readonly>
    </form>
</body>
</html>